76th United States Congress
Senate

State (class)
Vacator
Reason for change
Successor
Date of successor's formal installation
Illinois (2)
J. Hamilton Lewis (D)
Died April 9, 1939. Successor appointed April 14, 1939, to continue the term.
James M. Slattery (D)
April 14, 1939
Kentucky (2)
M. M. Logan (D)
Died October 3, 1939. Successor appointed October 10, 1939, to continue the term.
Happy Chandler (D)
October 10, 1939
Idaho (2)
William E. Borah (R)
Died January 19, 1940. Successor appointed January 27, 1940, to continue the term.
John W. Thomas (R)
January 27, 1940
Vermont (3)
Ernest W. Gibson (R)
Died June 20, 1940. Successor appointed October 14, 1940, to continue the term.
Ernest W. Gibson, Jr. (R)
October 14, 1940
Minnesota (2)
Ernest Lundeen (FL)
Died August 31, 1940. Successor appointed October 14, 1940, to continue the term. Successor lost election to finish the term.
Joseph H. Ball (R)
October 14, 1940
Nevada (1)
Key Pittman (D)
Died November 10, 1940. Successor appointed November 27, 1940, to continue the term. Successor lost nomination to finish the term.
Berkeley L. Bunker (D)
November 27, 1940
Illinois (2)
James M. Slattery (D)
Interim appointee lost election November 21, 1940, to finish the term.
Charles W. Brooks (R)
November 22, 1940
Washington (1)
Lewis B. Schwellenbach (D)
Resigned December 16, 1940, to become judge of the U.S. District Court for the Eastern District of Washington.
Monrad Wallgren (D)
December 19, 1940

Question: When did James Hamilton Lewis (D), James M. Slattery (D), and  Charles W. Brooks (R) were formally installed?
Answer: James Hamilton Lewis (D), until April 9, 1939 James M. Slattery (D), April 14, 1939 – November 21, 1940 Charles W. Brooks (R), from November 22, 1940.